D uring the planning for President Trump’s latest strike on Iran, Britain refused to allow the United States to launch air attacks from the U.S.-U.K. base at Diego Garcia, an island in the Indian Ocean. Only a few hours’ flying time from the Middle East, Diego Garcia offers airfields long enough for the heaviest bombers and has naval docks large enough for aircraft carriers and nuclear submarines. It is British territory, left over from colonial times, but was jointly developed under a U.S.-U.K.